High-Tech Chain Mail

Story by David Booth// Photos by David Booth
October 12 2021

As strange as it may seem, Sir Lancelot and his boys ’round the table may have been on to something that could save the modern motorcyclist. No, I’m not suggesting we all attach a jousting lance to our bikes, the better to skewer all the idiots trying to turn left in front of us. Nor am I suggesting that there is some mythical motorcycling Holy Grail possessing magical healing powers. Rather I am talking about the chain mail the warriors — the most pure of them all, of course, being Lancelot — used as protection when they went into the inevitable sword fights and jousts that are part and parcel of a quest. Leaving aside the questionable effectiveness of period-piece chain mail as protection against even the crude weapons of the day, no other than Motorcycle News seems convinced that something closely resembling those medieval links of steel could offer motorcyclists protection in the event of a crash.

According to a paper published by Nature Magazine the California Institute of Technology has developed a system, of chain mail-like interlocking octahedrons — structured fabrics with tunable mechanical properties — which, like those suits of old, are being developed as protection against weaponry; namely, against bullets, as the material is being developed for modern bullet-proof vests. Unlike the crude affairs of old, however, CalTech’s armour is truly high-tech. For one thing, those interlocking octahedrons are 3D-printed with optimized triangular faces. While current proof-of-concept prototypes are constructed of plastic, 3D manufacturing allows a wide range of even more robust materials, such as various metals and even carbon fibre.

What makes this modern chain mail truly magical, however, is not the intricacies of those interlocking bits, but rather their ability — D3O-like — to change state. Because they’re hollow in their free state, the links are completely flexible and able to move freely. However, when they are tightly packed, they become much more rigid: the gaps between links close and the entire armour becomes resistant to impacts. For instance, in its flexible state, the prototype chain mail deformed some 26 millimetres when a 30-gram steel ball was dropped on it. But, in its locked state, there was barely 3 mm of movement, the impact distributed over a much wider area.

One of the inventors, Chiara Daraio, a professor of mechanical engineering and applied physics at CalTech, likens the effect to coffee grounds. Loose, coffee grounds offer no tensile strength. However, if they are vacuum-sealed in a packing bag, the result is a “solid, via a process we call ‘jamming’” that can steadfastly resist impact. But, as we all know, “as soon as you open the pack, the coffee grounds are no longer jammed against each other, and you can pour them as though they were a fluid.” The idea, says Daraio, is “to make materials that can change stiffness on command,” very much like current D3O armour does when you fall off your motorcycle.

How this modern chain transforms, however, is much different than current armour. Unlike D3O, which, because it is a non-Newtonian fluid, hardens automatically when it is impacted, CalTech’s armour — like modern airbag vests — has to be told when to stiffen. Early prototypes have been encased in a flexible plastic envelope that draws the octahedrons into close proximity with each other when all the air is sucked out (hence the coffee grounds comparison). In more practical terms, CalTech’s researchers also say that something as simple as a string that quickly pulls the links together might be sufficient, depending on the speed of actuation necessary.

Whether CalTech’s discovery becomes practical for motorcycle clothing or not, it certainly does show promise. For one thing, it would seem to offer most of the pliability of D3O-like armour but with greater load-carrying capacity, as well as an ability to distribute any impact over a wider area.

It’s doubtful that chain mail, no matter how modern or computer-controlled, could offer the impact resistance of an airbag. On the other hand, it could prove far more comfortable. Air bags rely on, well, bags, which offer no permeability or venting, making them notoriously uncomfortable in hot weather. CalTech’s chain mail, in its relaxed form, is about as porous as the best mesh jackets, which means it should allow far more ventilation.

How much such protection would cost, especially if such protectors need the same costly actuators as airbag vests, remains to be seen, but it could offer an interesting compromise between comfortable passive armour and the impact resistance of protective, but bulky, air bags.

Could such a high-tech revision of the primitive protection garments we remember from folklore lead to a safer motorcycling future? José E. Andrade, the George W. Housner Professor of Civil and Mechanical Engineering and CalTech’s resident expert in the modelling of granular materials, makes a great case for the answer being yes:. “In this chain mail application, the ability to carry tensile loads at the grain scale is a game changer,” he says. “It’s like having a string that can carry compressive loads.” In simpler terms, that means that something even more flexible than current armour could be “trained” to also withstand the impacts of a motorcycle accident.

I wonder if it’s too late to start believing in the myths of the Round Table.


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